Phase change materials (PCMs) have been utilized as thermal energy storage systems for decades due to their ability to store and release energy in the form of heat during a phase transition, most commonly from the solid to liquid states. PCMs exist in many forms including organic, inorganic, eutectics, and solid-solid. With this wide variety, a range of temperatures for different applications can be achieved. It is important to have a PCM temperature in a workable range for the application in order to get the full charge of energy out of the system. These storage systems can be implemented in many different applications such as bedding, textiles, electronics, bio-tech, and pharmaceutical.
A commonly known application of energy storage is in the form of cold pack therapy. Cold packs are generally water based formulations that once active, keep their surroundings cold for a specified amount of time. They are commonly used as first aid relief, and food and beverage controlled refrigeration. Water is one of the best known PCMs due to its high latent heat value of 332 J/g, but water also has disadvantages. Water melts around 0° C., however, it can be super cooled to temperatures on the order of −40° C. Most commercial freezers only reach temperatures in the −23° C. to −15° C. range, which presents a problem for a water based formulation that requires freeze temps lower than that to charge the PCM completely.
While there are commercial products, such as instant ice packs, that base their phase change on the presence of water, its efficacy is often diluted by the other additives needed to improve the formula in other areas, like viscosity, and freeze temperature. Often times these additives dilute the enthalpy available of the water, therefore hindering its efficacy as a PCM.
There is a need for new and improved cold packs or other thermal cooling products that corrects the fundamental issues of using water as the PCM, noted above, in such products.